This invention relates to a package including a heat sink suitable for a ceramic substrate.
An example of conventional packages is disclosed in U.S. Pat. No. 4,398.208. Referring to FIG. 2 of the patent, the conventional package comprises an alumina-ceramic substrate 21, a plurality of integrated circuit (IC) chips 24 mounted on the upper surface of the substrate 21, a plurality of covers 22 covering the IC chips 24 and heat sinks 40 fixed to the lower surface of the substrate 21. Each of the heat sinks 40 used for the package is made of aluminum or copper. However, the heat expansion coefficients of aluminum and copper are about 24.times.10.sup.-6 (1/.degree.C. (centigrade)) and about 17.times.10.sup.-6 (1/.degree.C.), respectively, both of which are considerably greater than the heat expansion coefficient of ceramic (about 7.times.10.sup.-6 (1/.degree.C.)). For this reason, the conventional package has disadvantages that the heat sinks may come off the substrate and that cracks may develop in the substrate.
Another example of the conventional type packages is disclosed in the Japanese Utility Model Application Disclosure No. 91742/1984. A heat sink 5 used in the package is made of a copper-tungsten alloy or a copper-molybdenum alloy. Since the heat expansion coefficients of both alloys are approximately equal to that of the ceramic, the package is not affected by the above-mentioned coefficient difference. However, the package has a different disadvantage in that the weight of the entire package becomes considerably greater because the specific gravity of the copper-tungsten alloy and the copper-molybdenum alloy are no less than 16 and 9 (g(gram)/cm.sup.3 (cubic centimeter)), respectively. In addition, both the tungsten material and the molybdenum material are extremely expensive, resulting in a costly package.